Fog abatement

ABSTRACT

Disclosed is a method for dissipating a fog by modifying the fog particles with a chemical agent. An aerosol dispersion of the chemical agent is formed and passed through a device which shapes the dispersion into vortex rings. The vortex ring dispersion is then discharged from the device and directed into the fog, in which it modifies the size distribution of the fog particles to improve visibility.

United States Patent 1191 Lane et al. Apr. 16, 1974 [5 FOG ABATEMENT 2,934,275 4/1960 Ball 239/2 R 3,608,810 9 1971 K [751 lnvemrs= Gemge Lane Freeland Mlch? 3,715,319 2/1973 K322i: a1 239/2 R x Robert L. Williams; Ben A. Fortner,

[ Assigneez The Dow Chemical p y, 10,046 0/1924 India 239/14 Midland, Mich. OTHER PUBLICATIONS [22] Filed: Oct 13 1972 Kendig, Frank, The Science of Smoke Rings and Doughnuts, Saturday Review, March 18, 1972 Issue, [21] App]. No.: 297,468 Periodical, pp. 40-44.

[52] U.S. Cl. 239/2 R, 239/8, 239/14, im y in Ward,

239/399, 239/419.5, 252/305, 252/319 Attorney, Agent, or Firm-V. Dean Clausen; Lloyd S. [51] Int. Cl EOlh 13/00, B05b 17/04 JOWanOVitZ [58] Field of Search 239/2 R, 8-10,

239/14, 77, 399, 403, 418, 419.5, 428.5, [57] ABSTRACT 461; 252/305 319 Disclosed is a method for dissipating a fog by modifying the fog particles with a chemical agent. An aerosol [56] References cued dispersion of the chemical agent is formed and passed UNITED STATES PATENTS through a device which shapes the dispersion into vor- 3,722,815 3/1973 Moore 239/2 R tex rings. The vortex ring dispersion is then discharged 990.121 4/1911 Drake 239/2 R X from the device and directed into the fog, in which it 2.051625 9/1936 Houghto" A 3 1 1 239/2 R modifies the size distribution of the fog particles to im- 2,740,663 4/1956 Pomykala 239 2 R prove visibility 3,534,906 10/1970 Gensler 239/2 R 3,595,477 7/1971 Wollin et al. 239/2 3 Claims, 3 Drawing Figures 1; b 5-O- g Run B Q 8 4 0- U ".1

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FOG ABATEMENT BACKGROUND OF THE INVENTION This invention relates to abatement or dissipation of fog. More specifically, the invention relates to fog dissipation with an aerosol dispersion of a fog modifying substance which is discharged into the fog in the form of vortex rings.

The general public is well aware of the hazards to operation of aircraft and automobiles when fog occurs at airports and on highways. Because of these hazards, various techniques have been studied over a period of years in an attempt to disperse fog. One technique used at airports is to spray a fog modifying agent from a low flying aircraft, with the aircraft ordinarily making several passes through the fog. The aircraft dispersal technique has several disadvantages, such as high cost of aircraft operation, danger of flying in fog, and interference with normal airport operations.

A more preferred technique, therefore, is to disperse the fog modifying agents from a ground based system. In one of the ground based systems experiments have been conducted which involve blowing the fog modifying chemicals into a fog through a long funnel-shaped tube. One drawback to this method is poor lateral dispersion of the chemical agent into the fog. Another disadvantage is that dispersing the chemicals to higher altitudes requires expending considerable energy.

SUMMARY OF THE INVENTION Broadly, the present invention is directed to a method for dissipating a fog by modifying the fog particles. The first step is to form an aerosol dispersion of a substance which upon contact with the fog will initiate modification of the size distribution of the fog particles. Secondly, the aerosol dispersion is passed through a device adapted to form the dispersion into vortex rings. As the vortex rings are discharged from the device. they are directed into the fog to initiate accretion and, preferably, precipitation of the fog particles.

DESCRIPTION OF THE DRAWING FIG. I is a graph illustrating a comparison between normal fog decay and accelerated fog decay resulting from discharge of a fog modifying substance into a fog.

FIG. 2 is a graph illustrating a comparison of accelerated fog decay resulting from discharge of different amounts of a fog modifying substance into a fog.

FIG. 3 is a graph which shows the acceleration of fog decay achieved by discharging different amounts of a fog modifying substance into a stabilized fog.

DESCRIPTION OF A PREFERRED EMBODIMENT Suitable fog modifying substances which may be used in this invention include any of the organic or inorganic chemicals which will undergo accretion of particles at the expense of the fog particles. To state it another way, the chemical agent must have those properties which enable the particles of the chemical material, when dispersed into a fog, to grow as a result of absorbing the fog particles. One of the properties is that the chemical agent must be a liquid or solid which can be prepared as an aerosol dispersion. Another property is that the chemical agent in the dispersion must comprise particles which range in size from about 2 to microns in diameter. Dispersions having particles smaller than about 2 microns in diameter are undesirable, in that such dispersions have been shown to stabilize fog.

Typically, the chemical agent should be a hygroscopic or water soluble compound which will cause the fog particles to undergo a redistribution of particle size which will diminish obscuration and, preferably thereafter, to precipitate the fog particles. Typical inorganic compounds which may be used are the alkali metal salts and the alkaline earth metal salts, particularly sodium chloride, calcium chloride, potassium chloride and magnesium chloride. Especially preferred is sodium chloride having a particle size in the range of from about 5 to 40 microns in diameter. Representative of organic compounds which may be used are solid materials, such as urea, or liquid materials such as glycerine, ethylene glycol, or diethylene glycol. Other suitable compounds include organic polyelectrolytes, specifically polyalkylenimines, such as polyethyleneimine, polypropyleneimine, and the like. Reference is made to US. Pat. No. 3,534,906, which describes the polyelectrolyte compounds and other chemical materials with similar properties.

In the practice of the invention, the fog modifying chemical is first prepared as an aerosol dispersion. In general, an aerosol dispersion may be defined as a suspension of fine solid or liquid particles in a gas. Suitable conventional techniques and apparatus for preparing the dispersion include centrifugal atomizers, sonic agitation, pneumatic atomizers, hydraulic atomizers, spraying, vaporization, and the like. After the aerosol dispersion is made up it is passed through a device which shapes the dispersion into discrete vortex rings. From this device, the vortex rings may be discharged either intermittently or continually into a fog.

A vortex ring may be defined as a mass of fluid which flows in a circular pattern. The shape of the ring is generally toroidal and substantially circular in crosssection. One of the more familiar examples is a smoke ring, such as those produced by humans upon exhaling tobacco smoke. Another example is the burning powder rings which are formed when large military guns are fired. From past studies scientists have discovered that vortex rings provide very effective means of transporting one fluid through another. This is possible because of the circular pattern of fluid flow which makes the vortex ring an extremely stable structure. In the atmosphere, for example, vortex rings of smoke or other gaseous materials have been known to travel great distances before disintegrating.

The following examples are given to illustrate the invention, but are not intended to limit the invention to the precise embodiment described herein.

EXAMPLE I A chamber adapted to contain an artificial warm fog was utilized to test the fog modifying method of this invention. Basically, the chamber comprises a cylindrical tank about 29 feet long by 7.75 feet in diameter and closed at both ends. Positioned on the floor of the chamber near the center is a device adapted to make a vortex ring dispersion. More specifically, the device is adapted for receiving a solid or liquid material and converting the material into an aerosol dispersion in the form of vortex rings upon discharge of the dispersion from the device. A 250 Watt spotlight, which is controlled by an adjustable voltage transformer, is mounted on the far end wall of the chamber. The spotlight is positioned so that the light beam therefrom will pass lengthwise through the chamber and strike a selenium photovoltaic cell, which is mounted on the near end wall of the chamber.

Mounted at the top of the chamber are three 100 Watt overhead lapms, which are spaced equidistantly along the length of the chamber. Primarily, these lamps are used to provide illumination for the work to be done in the chamber. Another function of the lamps, as explained later in this description, is to enable a rough measure of fog density as fog is introduced into the chamber. Fastened to the side wall of the chamber at equidistant points are three 12 inch circulating fans. A steam line is connected into the chamber close to the top of the near end wall above the photocell. The purpose of the steam line is to inject steam into the chamber to create an artificial warm fog.

The spotlight beam is directed through the fog and onto the photocell to obtain a reading which indicates the density of the fog. Specifically, the reading is obtained by amplifying the photocell output with an amplifier, converting from voltage to frequency with a converter, and displaying the frequency as a counts per minute digital value on an electronic counter. Since the counts/minute values are directly proportional to the light intensity, the reading obtained is a good measure of the density of the fog. Based on the scale used in the present test procedure, a value of 1.00 counts/minute indicates a very dense fog, whereas a value above about 4.0 counts/minute indicates a very light fog.

A typical test procedure is generally as follows. The chamber walls are wetted down and the instruments are calibrated for background noise and 100 percent transmission (maximum count). Steam is injected into the chamber until the overhead lamp at the far end of the chamber becomes visibly obscured. The timer is started and the circulating fans are turned on to aid dispersion of the fog particles in the chamber atmosphere. The overhead lights are turned off, the spotlight is turned on and the voltage is adjusted to 127 volts. After a period of 1 minute has elapsed, the fans are turned off and the light intensity being picked up by the photocell is recorded as a function of time.

In this example a first series of five runs was made to determine the rate of normal decay of the fog. For the purpose of this test normal fog decay is defined as natural dissipation without addition of a modifying substance to the fog. The results are set out in Table 1 below under the heading Test A. The light intensity count values shown under Test A represent an average count for each of the five runs.

A second series of three runs was made to determine the rate of fog decay obtained by adding different amounts of the fog-modifying chemical to the fog. The chemical used was NaCl, finely ground, with a particle size range of from about 2 to 100 microns in diameter. For each run, the NaCl was added to the fog as a vortex ring dispersion for 2 minutes. The average amount added for each run was about 3.0 grams.

The results of these three runs are set out in Table I under the heading Test B. The light intensity count values shown under Test B represent an average count for each of the three runs. As shown in Table 1, a comparison of these light intensity values between Test A and Test B clearly indicates that adding NaCl to a fog, as a vortex ring dispersion, will decay the fog considerably faster than allowing the fog to dissipate under natural conditions. Data set out in Table I are illustrated graphically in the chart shown in FIG. 1 of the drawing.

TABLE I Comparison of Fog Decay from Normal Dissipation and from Addition of NaCl Test B Fog Decay after NaCl Addition Test A Normal Fog Decay 3 g. (avg) NaCl added to fog as a vortex ring dispersion for 2 minutes.

Example II For this Example two runs were made in which NaCl was added to the fog as a vortex ring dispersion. The particle size of the dispersion was in the range of from 2 to I00 microns in diameter. The amount of NaCl used in Run A was about 1 1.0 grams, which was added over a period of 5 minutes. For Run B the amount of NaCl was about 4.0 grams and the time of addition was 2 minutes. During the entire period of each run a steady flow of steam was added to the chamber and the center fan in the chamber was allowed to run continuously. Running the fan gives better dispersion of the fog particles in the chamber atmosphere.

Results are shown in Table 11. Referring to the data set out in Table II, for both Run A and Run B, it will be noted that the light intensity count increased sharply immediately upon adding the NaCl dispersion to the fog. The data would indicate, therefore, that the NaCl dispersion accelerates the fog decay significantly. A graphic illustration of the data in Table 11 is shown in FlG. 2 of the drawing.

TABLE 11 Decay of Fog from Addition of NaCl Run A Run B Time Light Intensity Time Light Intensity (minutes) (count value) (minutes) (count value) 5 0.71 5 0.16 10 0.72 10 0.18 12 Add NaCl 12 Add NaCl 13 1.81 13 0.68 14 4.95 14 2.48 15 5.36 15 Stop NaCl 16 5.54 16 2.63 17 5.30 17 1.92 Stop NaCl 1 1 g. NaCl added to fog as a vortex ring dispersion for 5 minutes. 2 4 g. NaCl added to fog as a vortex ring dispersion for 3 minutes.

EXAMPLE III This example relates to several runs in which the fog chamber was pretreated with a material capable of stabilizing the fog. The stabilizing composition used was an aerosol dispersion of KCl with a particle size in the submicron range. The aerosol dispersion was introduced into the chamber, prior to injection of steam to form the fog, by igniting a pyrotechnic composition which produces the KC] stabilizer compound. According to the practice of this invention, stabilizing the fog refers to modifying the fog with a substance which will inhibit the natural decay of the fog.

Run A represents the best stable fog conditions, which were obtained by adding about 3.0 grams of the KCl composition to the fog. The results are set out in Table III below and are illustrated in the graph in FIG. 3 of the drawing. Looking at the data for Run A, it will be noted that the light intensity count values remain at a low level for an extended period of time. The indication, therefore, is that the fog remains quite dense (stabilized) for this period of time.

In Run B the fog was stabilized in the same manner and with the same amount of stabilizing composition as employed in Run A. At the end of 19 minutes, when the fog had stabilized, about 5.0 grams of NaCl was added, as a vortex ring dispersion, for a period of 4 minutes. For Run C the fog was also stabilized under the same conditions employed in Run B. At the end of 19 minutes, about 3.5 grams of NaCl was added for a period of 4 minutes.

Results of Runs B and C are also set out in Table III and are illustrated in the graph of FIG. 3. Referring to the data for Runs B and C, it will be noted that the light intensity count increased sharply upon adding the NaCl dispersion to the fog. The conclusion is that the NaCl dispersion will substantially accelerate fog dissipation even though the fog has been stabilized.

TABLE III [Decay of stabilized fog from addition of NaCl] Run A Bun B Run C Light Light Light intensity intensity I intensity 'Iimo (count Time (count Inne (count; (minutes) value) (minutes) value) (minutes) value) 1 0 l. t 3 1. 28 3 2. 95 4 4 0. 03 5 0. 001 5 0. 023 0. 03 0. 054 15 0. 013 0. 07 19 0. 085 19 0. 31 0. l6 0.22 20 0.19 20 0. 44 0. 29 21 0.57 21 1. 10 22 2. 04 22 3. 71 24 3. 85 24 4.13

l 3 g. of u KCl aerosol dispersion added to log to stabilize tog condition. 3 Add steam.

3 5 g. of NaCl added to fog as a. vortex ring dispersion.

4 3.5 g. of NaCl added to fog as a vortex ring dispersion.

5 Stop N aCl.

In the practice of the invention any device suitable for receiving an aerosol dispersion of the fog modifying substance and dispensing the substance in the form of vortex rings may be used. The amount of the fog modifying chemical, the size of the dispersion vortex rings, and the rate of discharge of the dispersed rings into the fog bank, are dependent on several factors. Some of these factors are (l) the number of dispensing devices used, (2) the size of the fog bank, (3) the composition and density of the fog bank, (4) the distance of the fog bank from the dispensing devices, and (5) the velocity and direction of the wind.

Generally speaking, the present method is best suited for dissipating warm fogs. It is also contemplated, however, that the same technique may be used to dissipate cold fogs. Warm fogs are of two general types, radiation fogs and advection fogs. A radiation fog is formed by loss of heat from an air mass, so that the temperature within the air mass is lowered to the point that the air is super-saturated with water and a fog forms. Advection fogs, which occur frequently on a sea coast, are formed when a cold air mass comes in contact with a warmer air mass. As the warmer air is cooled, it becomes supersaturated with water vapor to form the fog. In a cold fog, the temperature of the fog mass is below the freezing point of water. The fog droplets are not frozen, however, but instead are supercooled.

What is claimed is:

1. A method for dissipating a fog by modifying the fog particles therein, which includes the steps of:

a. forming an aerosol dispersion of a substance capable of modifying the fog particles to an extent which will improve visibility; v

b. passing the aerosol dispersion through a device adapted to form the said dispersion into vortex rings; and

c. discharging the aerosol dispersion from the device in the form of vortex rings into the fog to thereby dissipate the fog particles.

2. The method of claim 1 in which the fog modifying substance is a member selected from the group consisting of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.

3. A method for dissipating a fog bank by modifying the fog particles therein, which includes the steps of:

a. forming an aerosol dispersion of sodium chloride in which the particles are from about 2 to microns in diameter;

b. passing the sodium chloride dispersion through a device adapted to form the said dispersion into vortex rings; and

c. discharging the sodium chloride dispersion from the device in the form of vortex rings into the fog to thereby dissipate the fog particles. 

2. The method of claim 1 in which the fog modifying substance is a member selected from the group consisting of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.
 3. A method for dissipating a fog bank by modifying the fog particles therein, which includes the steps of: a. forming an aerosol dispersion of sodium chloride in which the particles are from about 2 to 100 microns in diameter; b. passing the sodium chloride dispersion through a device adapted to form the said dispersion into vortex rings; and c. discharging the sodium chloride dispersion from the device in the form of vortex rings into the fog to thereby dissipate the fog particles. 